The objective of this multicenter double-blind, placebo controlled randomized study is to evaluate the safety and efficacy of multiple doses of r-h CuZnSOD to prevent oxygen toxicity & severe lung disease in neonates who require mechanical ventilation. At present there is only symptomatic treatment for oxygen toxicity. Surfactant therapy improves RDS (Respiratory Distress Syndrome) but not PBD (Bronchopulm. Dysp.), a chronic inflammatory condition of the lungs triggered by exposure to 02 in premature infants, who are known to have very reduced levels of antioxidant enzymes.